Conventional techniques for rendering shadows using a graphics processor include using shadow maps. Shadow maps are stored in memory at a fixed resolution. When the distance from a viewpoint, e.g., camera, to a shadow decreases magnified shadow edges appear aliased, i.e. jagged, due to insufficient resolution of the shadow map. This type of aliasing is referred to as “perspective aliasing”. Storing the shadow maps at a high resolution will reduce the perspective aliasing, but requires more memory space for storing the high resolution shadow map. Computationally intensive techniques such as supersampling and accumulation buffer rendering may be used to antialias an image including shadows. Another type of aliasing, projection aliasing, results from light rays that are nearly parallel to the shadowed surface stretching a shadow along the surface. Using a high resolution shadow map is not sufficient to significantly reduce project aliasing because the stretching may be infinite.
Accordingly, it would be desirable to render antialiased magnified shadows without using shadow maps stored at a high resolution rather than using a lower resolution shadow map.